A Very Brief Note on Following the Presence of Biofuels in Fossil Fuels by Radioactivity Mesurements

[NNadir]

I'm catching up on my reading before focusing on a topic (later in the day) on the environmental behavior of plutonium at the Nevada National Insecurity Site, and came across this very cute and mildly interesting paper by scientists working (at Chevron) for the dangerous fossil fuel industry, an industry which I oppose (Chevron): Liquid Scintillation Counting Method for the Refinery Laboratory-Based Measurements of Fuels to Support Refinery Bio-Feed Co-Processing (Matthew Hurt, Josephine Martinez, Ajit Pradhan, Michelle Young, and Michael E. Moir Energy & Fuels 2021 35 (2), 1503-1510).

I'm not going to spend a lot of time writing about this paper, but here are a few cool excerpts about how the (disturbed) radioactive C-14 measurements, widely and famously used for carbon dating, apply to following the addition of biomass to dangerous fossil fuels:

With an ever-increasing need to reduce greenhouse gas emissions worldwide, there has been a regulatory push to start incentivizing the transition from traditional fossil fuels, such as crude oil, a high carbon intensity (CI) feedstock, to biologically sourced feedstocks that have lower CI.(1) To minimize costs while complying with the various government mandates, the goal for many in the petroleum refining industry is to utilize existing infrastructure.(2) It has been shown in a recent assessment that there is currently an abundance of low-cost biomass feedstocks that can be used to supplement crude oil to produce renewable fuels.(3) However, many traditional crude oil refineries are not equipped to handle a switch from 100% crude oil to 100% biological-based feeds because of process, catalytic, and metallurgical limitations of facilities.(4,5) To ease the transition from crude oil to bio-feeds and to comply with new regulations, some refineries have decided that the co-processing of bio-feedstocks into various reactor units in the refinery is the optimal way to proceed.(1,2,6) Co-processing bio-feeds, such as pyrolysis oil or vegetable oil, can be done in various locations, such as fluid catalytic cracking (FCC) and/or hydrotreating/hydrocracking units.(7?10) Recent pilot- and demonstration-scale studies using an FCC unit have demonstrated the viability of co-processing bio-oil with vacuum gas oil (VGO) in a refinery with FCC unit.(9?11) VGO is the distillation fraction of crude oil that requires vacuum to be applied to reduce the boiling point enough to evaporate the oil in the distillation column and typically has a boiling range of 800–1050 °F at standard temperature and pressure (STP). The Pacific Northwest National Laboratory (PNNL) conducted an assessment of all of the refineries in the United States on the flexibility of bio-oil co-processing capability using FCC, hydrotreating, or hydrocracking units and concluded that 95 out of 124 refineries have a total capacity ranging from 2900 to 232 500 barrels per day of VGO that could be used to co-process bio-feeds.(12)...

...14C is a radioactive isotope of carbon produced in the upper atmosphere through a neutron capture reaction by 14N atoms.(16) The production of 14C is relatively constant, with current atmospheric concentration changes due mostly to human activity either through the detonation of nuclear weapons (caused a spike in 14C concentration that peaked in the 1960s) or the excess production of CO2 through fossil fuel combustion (driving factor of current variation).(17,18) Living organisms take up all of the isotopes of carbon 12C, 13C, and 14C in the same proportions as they occur in the atmosphere for their life span.(19) For short-lived organisms, it can be assumed that the 14C concentration in the atmosphere is constant over the life span of the organism, which is a safe assumption for many fuel crops as they are typically harvested within 1 year of planting. It can also be assumed that crude oil has no 14C since the half-life of 14C is 5730 years, and crude oil is millions of years old.(1)
Commonly, refineries focus on running methods certified by the American Society for Testing and Materials (ASTM). There are currently two methods that are ASTM approved for the detection of 14C and are described in D6866 with the most recent version being D6866-20.

The authors note that the standard methods are expensive to run, and have a long lead time for turn around, and are not suitable for continuous processing, so they seek to find a fast convenient method that can be utilized as an in process control.

The expensive method, which was used for calibration:

All samples were sent for analysis to the Center for AMS at the Lawrence Livermore National Lab (LLNL), Livermore, CA. The facility has extensive prior experience testing fuel type samples and was involved in a previous AMS interlab study analyzing biofuels.(35) The LLNL AMS facility analyzed the samples according to ASTM D6866-18 Method B.(36) Using the 14C to 12C ratio, the data was reported in raw percent modern carbon (pMC). The raw pMC was then corrected using the 13C to 12C isotopic ratio measured by isotope ratio mass spectrometry (IRMS) instead of the results collected by the AMS for more accurate results. Choosing the correct reference year is very important to generate the most accurate results as the atmospheric concentration of 14C is slight changes over time.(36) The reference year of 2018 was used to correct for atmospheric 14C concentration for when the plants were grown; the 2018 pMC correction is 1.005 in accordance with ASTM D6866-18.(36) The data was further corrected by running a laboratory-supplied pure petroleum diesel sample, since previous studies showing blank correction help with accuracy.(35)

The cheap fast method using ambient radioactivity:

LSC was performed using a Hidex 300 SL automatic liquid scintillation counter super low-level system with active guard and temperature control modules. The samples were prepared by mixing 15 mL of the sample with 5 mL of Ultima Gold F scintillation cocktail and analyzed for 5 h. The counter was set to count between channels 100–400 to help maximize the signal-to-noise ratio instead of using the full 14C range between channels 5 and 650. The triple mode was used to reduce background noise further. The triple mode only counts photons that hit all three detectors at the same time; this is a unique feature of liquid scintillation counters that contain three photomultiplier detectors. Currently, Hidex liquid scintillation counters are the only commercial LSC instruments having three detectors. Once the samples are mixed, they are placed into the autosampler for a minimum of 1.0 h before running to minimize the chemiluminescence of the sample.

According to the conclusion of the paper, it worked quite well:

The goal of this study was to find a method to measure biocarbon content by 14C analysis that can easily be incorporated into a refinery laboratory, which yields comparable results to AMS, and has biocarbon detection limits between 0.53 and 0.72% depending on sample type. The use of a liquid scintillation counter with TDCR capabilities allows this to be achieved by removing the traditional and tedious sample preparation procedures. For these experiments, the use of a Hidex 300 SL LSC with a 5 h analysis time yielded data with an excellent correlation to AMS. As the absolute error for LSC increases with an increase in biocarbon concentration, method repeatability was calculated for two separate ranges, 0–20 and 20–100%. The calculated repeatability values are the method detection limit for each of the sample sets. For LSC results, the repeatability was calculated to be 0.72, 0.53, and 0.67% biocarbon, respectively, for the gasoline, diesel, and jet fuel standards, for the samples below 20% biocarbon, and for the samples above 20% biocarbon, the repeatability was 1.33, 1.41, and 1.33%, respectively.

Although I oppose fossil fuels, I believe that a possible means to keep some essential self propelled vehicles, rescue vehicles, farm machinery, transport trucking, using thermally reformed biomass (as opposed to fermented biomass such as ethanol as currently produced). This suggests, therefore some useful information, especially to detect cheating by the addition of dangerous fossil fuels after a regulated dangerous fossil fuel phase out, which is urgently necessary.